Exhaust gas treatment devices, e.g., catalytic converters and particle filters, have at least one insert, which is arranged in a tubular housing. In particular, inserts made of ceramic materials are known. Metallic inserts are known as well. It is common to arrange the particular insert in the particular housing by means of a mounting mat enveloping the insert. This mounting mat has a plurality of functions. On the one hand, it absorbs lateral accelerations, to which the exhaust gas treatment insert may be exposed during operation. On the other hand, the mounting mat can form a thermal insulation in order to reduce the thermal load of the housing. Furthermore, fixation of the position of the insert in the housing is regularly achieved with the mounting mat. The mounting mat must be pressed for this purpose radially between the insert and the housing. For the radial pressing of the mounting mat, it is known that the insert wrapped into the mounting mat can be pushed axially into the housing, and the housing still has an excessively high internal cross section in this state. The housing is subsequently compressed, i.e., radially deformed, until the desired pressing of the mounting mat is achieved.
In case of ceramic inserts, especially when they are designed as a monolith, the radial pressing of the mounting mat is comparatively problematic, because damage to the ceramic inserts may occur when excessive forces occur. This is combined with the circumstance that the inserts, especially ceramic monoliths, may have comparatively great shape tolerances, as a result of which local stress peaks may develop during the radial deformation of the housing. Furthermore, a radial gap, which is formed between the particular insert and the housing and is filled by the mounting mat, may have a nonuniform, radially measured gap dimension in the circumferential direction. In case of unfavorable tolerance chains, the gap dimension may now become so large that the mounting mat will not be pressed there sufficiently, which may cause the mounting mat to become detached during operation at this insufficiently pressed location, as a result of which a bypass bypassing the insert is formed in the housing.
A process for preparing catalytic converters, in which a rupture characteristic of the ceramic monolith, which depends on the particular combination of ceramic material and mounting mat material, is first determined, is known from U.S. Pat. No. 6,954,988 B2. This rupture characteristic contains especially the dependence of the forces occurring during the pressing of the mounting mat on the velocity at which the pressing is carried out. The pressing of the mounting mat is carried out in the prior-art process such that damage to the monolith is avoided.